How did Galileo contribute to our understanding of the universe?

Galileo was the first person to use a telescope to study space. Even though his telescope was weak by modern standards, he was able to observe amazing cosmic sights, including the phases of Venus, mountains on the Moon, stars in the Milky Way, and four moons orbiting Jupiter. In 1609 he published his discoveries in The Starry Messenger, which created a tremendous stir of excitement and controversy.

Galileo’s observations and experiments of terrestrial phenomena were equally important in changing human understanding of the physical laws of the cosmos. According to one famous story, he dropped metal balls of two different masses from the top of the Leaning Tower of Pisa. They landed on the ground at the same time, showing that an object’s mass has no effect on its speed as it falls to Earth. Through his works A Dialogue Concerning the Two Chief World Systems and Discourse on Two New Sciences, Galileo described the basics of how objects move both on Earth and in the heavens. These works led to the origins of physics, as articulated by Isaac Newton and others who followed him.